Direct Genetic Transfers from Aegilops squarrosa L. to Hexaploid Wheat1

Methodology of direct genetic transfer from diploid Aegilops squarrosa L. (2n = 14) to cultivated wheat (Triticum aestivum L.) (2n = 42) was explored as a possible applied plant breeding technique for rapid introgression of useful traits. One or more plants of 31 accessions of A. squarrosa (selected for resistance to certain pests of cultivated wheat) were crossed with ‘Wichita’ or ‘Newton’. A total of 219 hybrid embryos were cultured on a synthetic medium to overcome interploidy hybrid embryo‐endosperm incompatibility. Of the 219 embryos, 114 from crosses involving 17 accessions did not grow and were lost. However, one or more hybrids were obtained from crosses involving the 14 other accessions, and 24 F, hybrids were grown to maturity. The F,s were male sterile, but backcross (BC) progenies included fully fertile and meiotically stable 42‐chromosome plants. The partially fertile BC1 plants had a chromosome number range of 40 to 50; 50% with 2n = 40 to 42 and another 50% with 2n = 49 to 50; the latter arose from the functioning of restitution gametes. The probability of transfer of A. squarrosa genes from an F1hybrid to a single BC1 plant is 0.75. The BC1 and BC2 progenies segregated for several phenotypic traits and several lines with resistance to Hessian fly (Mayetiola destructor Say) biotype D, greenbug (Schizaphis graminum Rond.) biotype E, and leaf rust (Puccinia recondita Rob. ex Desm. f. sp. tritici) culture PRTUS6 were selected. Thus, the use of the embryo rescue method facilitated direct genetic transfers from A. squarrosa to hexaploid wheat, and thereby averted the need of using bridging species or prior synthesis of T. turgidum/A. squarrosa amphiploids to overcome interspecific cross‐incompatibilities.